I have posted this response twice in the last week

Did this job myself last week on my W124 M103 260e. Water pump was O.K. just a leak from the bottom.
What a barsteward of a job to replace a $ 3.00 O ring. The Aircon hoses are in the way of the rear bolts of the pump.
While removing the components to get at the pump I rocked the water pump pulley back and forwards to determine whether or not the pump front bearing was O.K. The rocking backwards and forwards of the pump exacerbated the O ring leak and it was quite easy to see coolant dripping out from the bottom area of the pump and not the bearing assemblies. The rubber O ring between block and pump body flat, hard and leaking


Items removed to facilitate job: Fan shroud, fan and clutch, fan and power steering pulleys, Dipstick and tube removed, belt tensioner, power steering moved out of the way, removed distributor to get at bolt holding heating tube to block, first two injectors and lines, moved IACV out of the way, radiator hoses.
Time taken to complete entire job 8 hours - including time to look for dropped bolts hidden in inaccessible locations

New items: O ring for pump body, O ring for heater tube, new bypass hose between block and thermostat housing, lower radiator hose.

Ivanerrol recommends purchasing a flexible extension - extremely handy.